And the bones of a ship on the bottom there is the highlight of any dive trip to the reef. The Yongala lies 100 feet down and is encrusted in coral, her ghostly deck both hauntingly beautiful and a reminder of just how alien and hostile the sea can be to humans.

When in October 2003, the latest of those divers boarded their home at sea for a week of reef exploring and cruising, none could imagine the horror that awaited one of them. The Yongala was about to claim another victim.

Among the guests that week were two American couples, great friends who'd been diving together for 25-years. Ken and Paula Snyder and Ginger and Doug Milsap.

They were introduced to the crew of the Spoilsport, as their big catamaran was called, then mixed and mingled with the other guests.

Paula Snyder: They had little champagne and fruit-type thing going on. And that's where we met Tina and Gabe.

Tina and Gabe Watson turned out to be young honeymooners from Alabama. Gabe was the seasoned diver of the pair. Bubbly, smiling Tina was a novice. A pretty bride.

Dennis Murphy: They looked like a good couple to you?

Ginger Milsap: They looked great. I remember Tina being very loving and complimentary toward Gabe.

Paula Snyder: She was just an absolute little princess. And he was tall and strapping and, you know, here they are on their honeymoon. And it was sort of, "Oh my gosh. Aren't they cute?"

The wedding, just 11 days before back in Alabama, had been just as romantic as the one Tina had long dreamed about.

Her mom and dad were as proud as they could be of their beautiful girl.

Amanda Phillips: She looked at me and said “I’m a princess bride” and I said, "You sure are." And she left with her dad in the limo … I think I cried almost all day long. It was the last one of my girls to get married.

Tina’s maid of honor and best friend from high-school, Amanda Phillips, was surprised that Tina would choose to go diving on her honeymoon.

Amanda Phillips: I would have said that she would have wanted to go to Europe, or you know, done like, castle tours or done something in the Caribbean, but she said that she wanted to go see the "Nemo" fish. And she wanted to see the sea turtles and go see Nemo.

Gabe had given Tina notice when they were dating that she was going to have to pick up on some of his hobbies -- fishing and scuba diving, for instance -- if they were going to grow together as a couple.

Cindy Thomas: I worried, and she would say, "Mom, he's a certified rescue diver. You do not have to worry.

Now with her bridegroom Gabe as a dive-buddy, Tina and the other guests settled into their cabins as the Spoilsport motored into the night. The next morning, they awoke to find themselves moored above the first of the dive sights, the much- anticipated wreck of the Yongala.

The dive master briefed the guests on what to expect below: the visibility, the currents. He reviewed the safety procedures.

Tina on her wedding day.

Ginger Milsap: Everybody just anticipates, you know, the ultimate dive.

Diving the Yongala follows a very set routine. It's not exactly an amusement park ride, but close.

Divers are taken out by an inflatable to a buoy.

Once in the water, they follow a permanent chain down to the bow of the wreck, where it's anchored.

The divers let go of the chain and then let the prevailing current carry them some 300 feet over the deck.

In scuba, this is called a drift dive. When they've taken in the wreck, they grab the second chain anchored off the stern and pull themselves back up to the surface where another dinghy is waiting to take them back to the big boat.

A few minutes after Gabe surfaced, the veteran diving friends looked across the water at another dive boat that had anchored nearby. And there on its deck they could make out someone giving CPR to a lifeless female diver. It was Tina, the bride of 11 days.

Ken Snyder: We could see her body on the deck of the Jazz II and see the physicians working on her.

Dennis Murphy: Did you see Gabe?

Paula Snyder: I went over and asked him if I could do anything for him. And he just said, “Well, I need a hug.” So I gave him a hug and I held him.

Nineteen minutes passed. The doctors still hadn't given up.

Another tourist on the dive that morning snapped an underwater pic and unwittingly captured an image of Tina Watson, lying on her right side on the ocean bottom, no bubbles coming from the regulator in her mouth.

The dive instructor accompanying that photographer realized immediately someone was in serious trouble. He kicked down to 100-feet and recognized that it was one of his guests, Tina, with her eyes open but unresponsive. He scooped her up and made his way to the surface as fast as he could. But the doctors topside could not resuscitate her. At 11:21 a.m. on Oct. 22, 2003, Tina Watson was declared dead.

One of the doctors who'd worked on Tina, to no avail, crossed the short distance to the Spoilsport and broke the news to her husband.

Paula Snyder: Gabe just said, "Are you kidding?" and we were standing up at that point. And we just all held each other and just fell down. I mean, we were just in disbelief. it was just tragic. Just tragic.

Half a world away, in an Alabama suburb, the family of the bride they'd seen off on her honeymoon not two weeks before were hearing news that was, well, simply unbelievable.

Tina’s dad, Tommy Thomas, was out of town on a business trip when Gabe’s father reached him.

Tommy Thomas: I answered the cell phone. And David, Gabe’s father, said, “I don't know any other way to tell you this. There's been an accident. Tina drowned. Here's my pastor." And he handed the phone to his preacher. And I just--

Cindy Thomas: Went to your knees.

Tommy Thomas: I went to my knees. I couldn't even think at the time to ask what happened, you know?

In a daze he made his way to the airport and the plane that would take him home to Alabama. It was his greatest hope at that moment that at least he'd be able to break the awful news to his wife Cindy and daughter Alanda and in person.

But Alanda had, by then, already arrived at work. She knew as soon as she walked in something had happened. Something bad.

Alanda Thomas: Everybody was looking at me crazy. And asking me if I was OK. And I was like, "What are y'all talking about?" Nobody really wanted to tell me what was going on.

Her boss told her to call her father. It was about her sister.

Tommy Thomas: And she went, "Daddy, what happened to Tina?" And it just broke my heart for her. I said, "How did you find out?" And she said, "I walked into work. And everybody knew but me." And that just blew me away. We had just found out.

Alanda Thomas: And I was scared that my mom would get up and hear.

Dennis Murphy: You had to tell your mother?

Alanda Thomas: Right after finding out myself. Yeah. But I just couldn't imagine her getting up and finding out by, you know, someone leaving a message on the answering machine.

Cindy Thomas: I was up in bed. I was sleeping late. And she came in the room. And I saw, I mean, her face. And what went across my mind first was -- because of him traveling -- was something had happened. And she said, "Mama, it's Tina." And she was just crying. She was bawling. And she said, "It's Tina. She's dead."

The shock wave was tearing through the Thomas family. In those first confusing moments, Cindy Thomas managed to reach Gabe’s mother. Cindy said she told her that she was on her way to the airport at that moment to fly out to Australia.

Cindy Thomas: If I'd have been in my right mind, I'd have been thinking, "OK, how would you already have made all your arrangements if you just found out?" But, I was just thinking, "OK, she's going." And I said just, "Please hold my baby when you get there. Just hold her."

It was dawning on Tina’s parents that they'd been the last to find out. They would learn later that Tina had been dead for some 12 hours before they started getting phone calls.

Finally with the intervention of the American consulate in Australia, the Thomas family reached the person they needed to hear the story from most, Tina’s new husband, Gabe. It was then nearly a full day since Tina had drowned. Father, mother and sister were all on the phone line together.

Tommy Thomas: Cindy started the conversation. And she asked him several times if he was doing OK. If he was all right.

Then Gabe told them the information they were desperate for: what had happened to Tina. This, they say, was his story: the couple was down about 40 feet when Tina gave her husband the thumbs up signal to surface. So he took her hand and headed back to the anchor rope, but halfway there she started sinking. Her hand reached out, knocked his mask loose, and Gabe had to let go of her to adjust it. With the mask in place, he saw his wife, sinking to the bottom faster than he could swim for her, so he surfaced for help.

Tommy Thomas: We've had that picture in our mind for a long time, of him going down after her, and her looking at him with her arms stretched up towards him

Alanda Thomas: And I felt sorry for him, you know, to have to live with that forever.

Cindy Thomas: A 26-year-old girl who is on her honeymoon thinking that she's starting her whole life. And then, it's snatched away in an instant. How do you wrap your head around that?

Tina in a wedding dress on a Saturday, thinking herself the princess bride.

Less than four weeks later, she was being eulogized.

Dennis Murphy, Dateline NBC: When was the last time you two saw her?

Tommy Thomas: Her and Gabe had gotten on the elevator to leave the reception. And I grabbed her and I told her I loved her and I said, “Baby girl, go have the time of your life.” And I turned around and grabbed Gabe and said, “Take care of my baby girl.” And that's the last time I saw her.

Her best friend, Amanda, said goodbye to the girl she used to model with, vacation with, dish about boys with.

Dennis Murphy: You see just the way she looked?

Amanda Phillips: I see her the way she looked when we were just hanging out. I don't see her in her wedding dress. No make-up, no nothing. Just hanging out with a big smile on her face.

In the days following her death, Tina’s dad, Tommy, had called down to Australia to talk to the water police. He told an officer there named Glenn the brief details of Tina’s drowning that he'd learned from his son-in-law.

Tommy Thomas: And I asked Glenn if that sounded like what he was told. And instead of just telling me, “Yeah, it was a horrible accident.” He said, “Well, that's one thing that we'll look at."

Dennis Murphy: What did that tell you?

Tommy Thomas: It was kind of hard to catch it, but it was like these guys are concerned about something, you know? And I just wish they'd tell me. And I couldn't pin him down to anything. He wouldn't really tell me anything at that stage.

But there were some people who wanted to talk to Tommy in just the worst way, four people he didn't know, the veteran divers, the two American couples aboard the Spoilsport that week who were so taken by the young honeymooners and that pretty, vivacious bride.

But when they finally did speak Ken, the vacationing diver, and Tommy, the father of the drowned woman, agreed to meet at the end of November 2003, about a month after Tina's death. It was a planned cup of coffee and a brief chat ended up lasting four hours.

Tommy Thomas: I said, you know, the thing that just haunts Cindy and I the most is the thought of Tina going to the ocean bottom with her arms stretched up toward Gabe looking at him, and him looking at her, and him turning to leave her, wondering what was going through her mind.

Ken Snyder: And I said, "Tommy, you can rest assured, that was not her last sight. Because that didn't happen." And he stared at me and I said, "Tommy, I don't know what happened underwater, but that didn't happen.” And I told him the conversation that Gabe had with me and with Doug.

It was a conversation that took place on the Spoilsport shortly after Gabe had come out of the water without his wife. The men say Gabe told them how Tina had panicked, his dealing with the mask and regulator, that he had lost hold of his wife, her sinking to the bottom, and his apparent inability to catch up to her as she dropped.

Doug Milsap: And I remember saying, you know, “Ken? I feel terrible about this, but something doesn't smell right here. This story is just not right."

Ken Snyder and Doug Milsap are divers with 25 years of experience and both can claim the highest level of certification in their sport: dive master.

Ken Snyder: He said “She was below me 10 feet or so with her arms outstretched, sinking feet first. And I had to make a split-second decision whether to assist her or go to the surface and get help.”

Dennis Murphy: I'm not a diver. Sounds plausible to me.

Ken Snyder: None of his story was plausible, in fact. My blood pressure got up at that point. And I said, "Gabe, you left her?" And he said, "I had to determine that I needed to go get help." And I said, "Gabe, that didn't happen. You better come up with something else. Cause that story didn't happen.”

Dennis Murphy: And the reason it couldn't happen?

Ken Snyder: Four or five things. She clearly could have panicked.

Doug Milsap: Panicked divers don't relax and raise their hands up in the air and look at you placidly saying, "Goodbye." She's going to be either clawing for his air supply or going for the surface.

Ken Snyder: Dead people sink.

And why, they wondered, couldn't Gabe reach his wife when she was only 10 feet beneath him?

Doug Milsap: Ten feet is a pittance underwater. It's two fin kicks and you're on top of her. There's absolutely no reason why he couldn't have followed her down.

And then the two said Gabe told them something that, in their experience, seemed inconceivable. Gabe said that Tina was too heavy for him.

Doug Milsap: He said “I reached out and I had a hold of her. And she was—“

Dennis Murphy: That's the buoyancy vest?

Doug Milsap: The buoyancy compensator. "I had a hold of her BC. And she was too heavy. And I couldn't hold on to her and I lost my grip on her and she started to sink."

Dennis Murphy: You challenged him at that moment, didn't you? What did you say?

Doug Milsap: I told him it was B.S. because underwater as long -- if your feet are not braced on the bottom there's no sensation of weight.

Doug remembers Gabe then tweaking his story.

Doug Milsap: And said, "Well, I had a hold of her and I was kicking and I was trying to pull her toward the surface. And at that point, she was too heavy. And I lost my grip on her and she started to sink."

Doug Milsap: Well, he kind of looked confused and astonished and wanted to know why I felt that way. And when I told him the first time, he changed his story. When I told him the second time, our conversation kind of ended.

And as the Thomas family remembers it, Gabe had said something to them that turned out not to be true. He said that he was right by his wife's side as she lay on the deck of the boat slipping away.

Tommy Thomas: He said he was holding her and calling to her while they were trying to resuscitate her.

Ken Snyder: He never went over to her. That would have been a normal male response. He would have jumped over the side of the boat and swam to his wife, just would have went to her. I mean, if you deserted her once, you wouldn't desert her again. I mean, it was just unbelievable.

Tommy Thomas: He didn't go over until after he knew she was dead.

Doug Milsap: None of this makes sense and it all indicates that he's not telling the truth about something.

The police would soon have the same feeling,

Brad Flynn: They could not say, "We look at this as being just an accident."

Divers from across the world continued to dive the wreck of the Yongala day in and day out, but onshore, Australian authorities were still troubled by the death of the young American honeymooner there months before.

The police seemed to have an easy set of facts before them: a marginal novice diver in over her ability who then panicked and drowned. And yet, they could not rule that death accidental.

The matter of Tina Watson remained an open investigation.

And the question that would not leave the investigators' minds was this: had she died as a result of foul play?

This question police were asking was not much different than the one posed by the dead woman's father back in Alabama.

Tommy Thomas: I would like to know exactly what happened. The two of them went in the water together and he came up without her. A lot of this doesn't make sense.

The Australian police advised Tommy Thomas to involve his own local police force on the case.

And that's how detective Sgt. Brad Flynn of Helena, Ala., became involved in a case 9,000 miles away. The dead woman's father asked for help in understanding what was shaping up as a mysterious drowning on the Great Barrier Reef.

Dennis Murphy, Dateline NBC: What was he asking you to do?

Brad Flynn: Find out what happened to my little girl.

The Aussies, he learned, were looking askance at the husband, Gabe’s, story.

Det. Flynn, who doesn't dive, who'd never been to Australia, was able to quickly get past the Down Under lingo and speak to his counterparts there in the international language of police procedures.

Det. Flynn learned that his counterparts in Australia were looking askance at the husband, Gabe’s, story.

Brad Flynn: And it was after they had spoken with him that they started kind of raising their eyebrows a little bit and saying, "I think we need to look into this a little bit more. Some things just aren't -- I don't get a good feeling with this."

What was perplexing the authorities down there was not just Gabe’s story, but the story told by a dive computer, a vital piece of gear for any scuba diver. When you learn how to read it, it will tell you critical information, like how deep you are, how many minutes of air you have left. And it does something else: a memory chip inside will describe the dive you've just made when you return to the surface. If you went down, say, 60 feet, this thing, the dive computer, will show you exactly that.

(Police tape)

Gabe Watson: Just turned and kicked and shoot straight back ... right up to the top.

Gabe's problem was that the story he told of his dive with Tina, didn't match the dive recorded on his computer.

Gabe aborted his first dive that morning with Tina. When he got under, he said, his dive computer started "beep beeping" a malfunction. The two had to surface.

Brad Flynn: This is where red flags start popping up. His statement was that when he got back to the boat, he realized that the batteries were in backwards.

Gabe Watson: I pulled the battery out, swapped it around, hooked it back up…

Brad Flynn: I've never seen any electrical device that operates whatsoever if the batteries are in backwards.

The Australian police tested that common-sense theory and, sure enough, with the batteries put in backwards in Gabe’s dive computer, the thing didn't work at all. There would have been no underwater "beeps" and that aborted dive wouldn't have been recorded at all.

But it had recorded the first dive. It showed Gabe going down a few feet, then coming back up.

Brad Flynn: It registered. It was downloaded. The information from that dive was downloaded by the Queensland police.

Dennis Murphy: So if this dive computer is working, but he tells Tina, "We've got to go back up.” Why would he do that?

Brad Flynn: That's the million-dollar question. Gabe and Tina were the only two people there. And we're having to backtrack to fill in the pieces here.

So now the cops were comparing the statements made by Gabe in his video with the statement made by the dive computer, and they weren't matching up.

This is how Gabe described his desperate attempt to reach Tina as she fell to the bottom.

(Police tape)

Gabe Watson: I went down. Started kicking down and I was kicking down but as fast as I was kicking down to go get her, she was ... she was going down just as fast.

But the dive computer said that never happened. It showed no attempt to sharply descend after Tina.

And it also contradicted his account of bursting to the surface after he'd made the decision to go for help ASAP.

(Police tape)

Gabe Watson: So from that point, I just ... I pretty much just turned and pretty much just rocketed to the top and, you know, I'm amazed that I didn't end up with the bends or something.

Seasoned divers say that's a snail's pace. A safe ascent from that depth could be made in 45 seconds to a little over a minute.

Brad Flynn: To say that it's slower than his bubbles were ascending is-- is truly an understatement.

Compare Gabe’s recorded rise with that of the dive instructor who pulled Tina off the bottom. Even carrying her, the instructor was able to ascend 100 feet in a minute-and-a-half, while Gabe’s recorded ascent of only 45 feet took between two and three minutes. It's a pro's skill versus a recreational diver's, but still -- police said when you factored in the guy was after all supposedly getting help for his wife, 45 feet, five deep ends of the swimming pool?

Brad Flynn: It's been red flag after red flag after red flag. And if he did what he said he did, we should be able to verify that. But every step that we took, we found more differences, more things that we could not explain, that he couldn't explain.

And there was another red flag: this videotaped statement was made at Gabe’s request.

It was about the water current by the Yongala.

(Police tape)

Gabe Watson: I just can't help but think that that the fight against the current is what allowed whatever thing took place that caused her to black out or whatever, and sink.

He'd bought a book at the local aquarium, researching the prevailing currents, and he told the police he was now sure that they at least partly explained Tina's drowning.

(Police tape)

Gabe Watson: We still don't know what physical thing happened with her. You know, I keep thinking you know had the current not been there, you know we'd still be out on the boat diving.

Brad Flynn: In his first statement, they ask him, on a scale of one to 10, what was the current like? He says, "a five." He said, "if it would've been much stronger, I don't think a novice diver," implying Tina, "would've been able to handle it." Several days later, he shows back up at the police station .

(Police tape)

Gabe Watson: We both realized once we both got in the current that that's too much.

Brad Flynn: He starts talking adamantly at how severe the current was.

Dennis Murphy: So he's researched the current?

Brad Flynn: Yeah. After the fact.

(Police tape)

Officer: Just tell us what it is...

Brad Flynn: If somebody shows back up, unrequested at my door, I’d like to talk to you about something I didn't mention before, is that going to cast suspicion? Absolutely.

Dennis Murphy: Is it possible that he's telling stories that sound nonsensical just because he's in an emotional panic and knowing that, your story's going to get jumbled up.

Brad Flynn: I can see that, but there are other parts of it that either he's told either the police or other witnesses that draw suspicion, even after the initial shock has worn off. And it should be clear in his mind what happened.

Dennis Murphy: The story's getting amended?

Brad Flynn: Yes. Changed after the fact.

And investigators knew that Gabe was certified as something called a "rescue diver." He'd taken a course in how to assist panicked and unconscious divers from under the sea. And yet, on that day, he'd opted not to go for his own bride.

And why couldn't police verify Gabe’s story that before he surfaced, he tried to alert other divers at the descent rope that he was in distress?

(Police tape)

Gabe Watson: I saw the people, I went up to them, you know, it was like grabbing a hold of them shaking them.

The honeymoon bride had drowned diving Australia’s Great Barrier Reef.

And before the authorities there, the Queensland police, could issue a finding of "accidental death," they needed to know more about why the story of the dead woman's dive-buddy, her husband of 11 days, was coming up inconsistent.

They'd taken statements from dozens of people who'd heard the husband Gabe Watson recount how he'd lost his wife that morning, forced to adjust his mask and regulator, only to see her drop helplessly to the ocean floor 100 feet down.

It was a kaleidoscope of differing accounts, according to the cops.

Dennis Murphy, Dateline NBC: How many different versions has he told so far of what happened underwater?

Sgt. Brad Flynn: With the interviews that I've done and the interviews that the Queensland police have done, approximately 16.

Dennis Murphy: Sixteen different versions?

Sgt. Flynn: With subtle variances.

The detective from a suburban town in Alabama, Sgt. Brad Flynn, found himself working in an official capacity with the Australian authorities as they probed the puzzling death of the local bride.

In addition to interviewing stateside witnesses who'd been on the dive boat that day, he decided he needed to know more about the couple themselves, Gabe and Tina, the young people who'd met as students at the University of Alabama.

Dennis Murphy: How far back do you go?

Brad Flynn: When they started dating. You paint a picture of someone and you paint a picture of the environment they're in.

Dennis Murphy: So you had to find out who Tina was.

Brad Flynn: Never met anybody that did not have just the best things to say about her.

Dennis Murphy: What's the picture that's coming together of him? Who does Gabe turn out to be to you?

Brad Flynn: Different. Very-- a man that likes to be in control, he knows what he wants and he goes after it. Everybody I've talked to has said that, "You know, Gabe does things one way: his way."

The detective learned that Tina's family thought Gabe a cool customer from the very first.

Tommy Thomas: He wasn't as outgoing with us as some of her boyfriends had been in the past. He had been going with her for quite some time, actually, and we had never met them before.

Cindy Thomas: I just flat told her. I said, "I've just got a really bad feeling. I don't like him." And she told me I wasn't giving him a chance. So, I said, OK, I will try to give him a chance. But we need to get to know him better.

Dennis Murphy: So mom doesn't like him. Dad?

Tommy Thomas: I was still trying to keep the peace. Because if this was the guy that Tina was going with, I wanted him to be a part of our family.

Alanda Thomas: Normally, with past boyfriends, you know, they were all about impressing me, knowing how close me and Tina were.

But Tina's kid sister, Alanda, got the distinct feeling that this new guy Gabe wanted her out of the picture.

Alanda Thomas: He had a problem with Tina being around me. Anytime I would be with her, he would be on the phone, I could hear him on the other end and he was not happy.

Dennis Murphy: What was the attraction? Her for him.

Tommy Thomas: She had just broken off a relationship and he was there. And she had, you know, all of her friends getting married. She joked quite a bit about being a bridesmaid.

Alanda Thomas: She felt old, which is really absurd. She could just see herself as an old maid with a bunch of cats. That's what she'd always say.

But best friend Amanda also remembers Tina began falling for the guy who bought her a Kate Spade handbag.

Amanda Phillips: She thought, you know, he was handsome. And, you know, a good guy. She loved his mother. And wanted to be a part of that family. And, you know, they had already accepted her very warmly into their lives.

In the fall of 2002, Tina told her sister that she'd discovered that Gabe had bought her an engagement ring.

And it's the weird business of the engagement ring that the family cites as exhibit a in their argument that Gabe was manipulative and enjoyed messing with Tina.

Alanda Thomas: My sister had gone over to his condo. and seen the jewelry bag sitting on top of the TV. And she had went over to it to look, and he had warned her that if she looked inside that he would take it back. And it stayed there for a good six months. Every time she went over there, she had to look at the bag.

Tommy Thomas: I said, "Tina just tell him to take the ring back. You know, you don't have to put up with that."

Cindy Thomas: This is something she would have never put up with, with anybody else. And I'm like, I don’t understand this. What's going on with my child?

Dennis Murphy: Was she a little embarrassed?

Amanda Phillips: I think she probably was, but she wouldn't have let anybody else know about it, you know? But it was something that ate her up.

It was only after Tina went to Atlanta one weekend to check out the possibility of a different boyfriend altogether that Gabe finally popped the question in April 2003.

Amanda Phillips: She went to see if there was a spark there, to see if there was any interest and, you know, ultimately it turned out there wasn't a spark.

To her friend Amanda, Tina seemed uncharacteristically deflated as she off-handedly spread the news of her engagement.

Amanda Phillips: There wasn't a big phone call. The, like, "Oh, my God, I'm engaged! This is wonderful!” It was, like, "Yeah. He proposed on Sunday.” I got the impression from her that she felt like she was settling.

Alanda Thomas: She told me that she loved him and he made her happy, so I was happy for her. You know, I was worried, too, though.

The detective learned that the wedding was set for that fall of 2003.

Gabe started shopping honeymoon destinations and that meant his non-diving fiancée would have to get herself certified in scuba.

Alanda Thomas: During the whole course of it, it was never something that she really seemed happy about doing.

She had to be good to go for the Great Barrier Reef.

Craig Cleckler: I told Tina that, "You've really got to do this, Tina, because you want to." And she made the statement, "You don't understand. I have to do this.”

Tommy Thomas: I was pretty concerned about the investigation. And I was just trying to find, well, what are you guys going to do next?

The investigation into the drowning of newlywed Tina Watson had moved from the water police to homicide detectives. In their view, it was no longer just a tragic dive accident. The police were viewing it as a suspicious death. The authorities were troubled by Gabe's apparently evolving stories were at odds with his own dive computer and dismissed by some seasoned divers as literally unbelievable.

Tina's family didn't even want to consider where the investigation was heading.

Tommy Thomas: It was very hard for me to get my head wrapped around the fact that there was any possibility that there could be any wrongdoing. I mean, why would you marry someone, go on your honeymoon and they'll die due to any wrongdoing on your part? It doesn't make sense.

Tensions were high when Gabe returned home to Alabama a week after his wife's death. And what were already fragile relations with Gabe snapped altogether by the time of Tina's funeral.

Brad Flynn: In speaking with the funeral directors, they said in all their years of conducting funeral services, they've never, ever done a service that had the tension and the drama that that one did.

And something very odd was going on at the cemetery. The flowers Tina's family placed on her grave kept disappearing. Tina's father began attaching them to the gravesite with wires. They disappeared again: cut free by a bolt cutter.

Sgt. Flynn had a hunch what was going on so he set up a video surveillance of Tina's grave.

And one afternoon he got this picture: Gabe arriving with bolt cutters and removing the flowers left there by her family.

Brad Flynn: I don't care what kind of issues I have with somebody. A grave is not a battle ground. That's not a place to wage a grudge match with in-laws, former in-laws. That's just dirty.

Dennis Murphy: Does it speak to your case, though -- his inexplicable behavior at the grave site, does that speak at all to what happened underwater in Australia?

Brad Flynn: It makes me look at it from a completely different perspective. I'm not saying that. I can use that to say, "Oh, you know, he's lying." But, yeah, it makes me look at him, his character, from a whole different point of view.

And Tina's father told the cops about Gabe's request to Tina before the wedding. It was about the life insurance policy she had through her employer.

Tommy Thomas: And I'm thinking, "Well, this is an odd time to bring this up."

According to Tommy Thomas, his daughter came to him and said that Gabe told her to increase her policy to the max: a $130,000 payout. And he wanted her to change the beneficiary from her father to him. Tommy told his daughter "tell Gabe that you've already taken care of all that,” but in fact he advised her not to deal with it until she got back from the honeymoon.

Tommy Thomas: I'd been in the insurance business at that time 25, almost 26 years. And I've had a hard time talking to people about their insurance coverage when they've been married for several years, much less before they even get married. So this is kind of strange anyway.

Amanda, Tina's best friend, had initially accepted her death as an accident, but when she got this Christmas card from Gabe just months after Tina's death, she wondered what was going on with Gabe, and severed all ties with him.

Amanda Phillips: It was a picture of Tina and Gabe at their wedding, and on the inside of the card, it said, "Who's that sexy guy standing next to Tina? Oh, yeah, that's me." Big smiley face on there. And at that point, I was done. That was too weird for me.

And all the while, that investigation in Australia was still open. Three years on, the police had decided to stage an underwater reenactment of Tina's drowning. A witness had come forward -- a doctor -- who described seeing Tina and another diver in a bear hug that morning. The police were going to test his story, one that implied foul play.

Cindy Thomas: You're laying in bed at night. You're seeing your daughter in the water. You're seeing her going down. And you can't help her. And you're thinking, I don't care what you tell me, nobody's doing anything. I would just go through those pha-- phases.

Tina Watson's parents had stayed on the Australian authorities. They'd made four trips there in the years since their daughter's drowning, trying to keep the investigation from going into the cold case file.

Finally, at the end of last year, an inquest was held to determine the cause and circumstances surrounding the young woman's death.

If the court determines there is enough evidence, it could send the case on for criminal trial.

Gabe Watson, the husband, was on the inquest's witness list.

Brad Flynn: They offered to pay all of his expenses to bring him to Australia to get him under oath to tell his story. He didn't show. Why? Not only that, it's the inquest into the death of his wife. Why don't you go? Even if you don't testify, why don't you go?

It was Gabe’s right not to testify, so his taped police interview was played instead. His conflicting statements were reviewed, and close to 70 witnesses testified. The inquest lasted four weeks, with the Thomases in court every day.

Tommy Thomas: I don't think I'll ever know exactly what happened. But I do believe that there is a version of events that were presented through the reenactment that could be very close to telling us the true story.

The reenactment became a primary piece of evidence for the inquest. Police divers spent three days diving over the wreck of the Yongala. In a series of dives, they attempted to reenact the circumstances of Tina's drowning.

Brad Flynn: They wanted everything to be as close to that day, the conditions, the equipment as they possibly could.

In the police reenactment video, a male diver about Tina's size was outfitted with the same gear she had on the day she died.

The divers began by laying down some markers: number one, the place on the ocean floor where Tina was found.

Then lines were laid out along the length of the wreck itself, replicating the course that Gabe and Tina swam that day, as he'd told the story in his police statement. The underwater path starts at the bow and ends a quarter of the way over the wreck by the ruins of the ship's mast -- as far as he said they got that morning.

The diver representing Tina went into a limp free fall, as Gabe had described her descent. They did it three times. And the question of the exercise was this: falling, with the current as it was, where would Tina have come to rest?

Tommy Thomas: If Gabe had been where he said that he was when the two of them parted, she would have landed on the deck--

And that's what the police found in their recreation. Each time the diver playing Tina was released, she ended up on or near the cargo hold of the sunken ship.

But that's not where Tina was found.

Tina was actually found 45 feet away from the rail of the ship.

Brad Flynn: Gabe’s version of what happened, of what where he said they were, and where Tina's body should have ended up, didn't add up. It didn't match up. It didn't mesh.

The only way Tina could end up where she did was if she swam out there away from the bow, or if someone took here there.

The inquest had also heard from a diver from a different boat than Gabe and Tina's. He'd testified that he'd seen a man giving Tina a face-to-face bear hug.

Sgt. Flynn: And he held her there for several seconds. She was motionless and let her go.

Murphy: Released her?

Sgt. Flynn: Released her.

The police recreation divers replicated what that witness said he'd seen, and they were also testing a theory of foul play that would explain why Tina simply dropped to the bottom without so much as a kick of the flippers.

Face-to-face, pinning the smaller diver's arms, the male diver would have been able to reach around, in theory, and turn off the other's air supply on the top of her tank. Tina's autopsy suggested that she might have suffered oxygen deprivation prior to drowning.

Tommy Thomas: What -- keeps running through my mind is something had to prevent her from going to the surface on her own. I think if she had been able to get there on her own, she would have done it, because she'd already demonstrated quite a survival instinct in her dive training.

This was the nightmare scenario in the theories of Tina's death. Had her air supply been turned off? Did she struggle and dislodge the mask of the person holding her? Did he momentarily lose his grip as she became unconscious and started falling? Did that other diver then see that divers from a second boat were in the water and coming toward him? Did that person turn Tina's air supply back on so that her gear would be found later to be in good working order?

That was exactly the theory offered to the inquest court by the lawyer for Tina Watson's parents.

Dennis Murphy: Is it still possible we're talking about a moderately competent diver here who just panicked?

Brad Flynn: Sure. But if that happened, why don't you tell us? Why don't you get that off your chest, you know. Why do you engage in this behavior? It just doesn't add up.

Detective Flynn, like most investigators who've looked at the facts, has trouble understanding a motivation for foul play here. They were newlyweds, with a seemingly bright future, and there was never a payout to the surviving husband.

Brad Flynn: We seem to believe that to have a murder, you have to have a motive of sex or money. None of that really comes into play here. But that doesn’t rule anything out. I have to follow the evidence regardless of where that leads me.

Last June, after hearing all the evidence, the inquest issued its findings. It determined that Gabe Watson should stand trial for murder. He was indicted, and a warrant was issued for his arrest. He was ordered to appear in court last February but he never showed. Then 3-weeks ago the Thomas family received a phone call.
Gabe had turned himself in to Australian authorities.

This past Monday, Tommy Thomas, his daughter Alanda, best friend Amanda and Detective Flynn all left Alabma and flew to Australia. Cindy Thomas was ill and unable to travel.

Gabe Watson--after five-and-half years--was in an Australian courtroom today to answer the charges against him.

What would he say about the mysterious events that ended his bride's life on the bottom of the Coral Sea?

Today in Australia, the investigation into Tina Watson's death that began on a reef at the bottom of the Coral Sea more than five years ago moved inland 700-miles south to an Australian courtroom in Brisbane.

Gabe Watson had turned himself in to face criminal charges. The Australian coroner determined that based on the all the evidence a jury could find Gabe Watson guilty of murder and the case should go to trial.

Attorneys for the Thomas's theorized that Watson had turned off the oxygen supply on his bride's air tank, then turned it back on when she was unconscious letting her drop to the ocean floor as he swam for the surface, a scenario replicated in the police divers' underwater reconstruction.

As Tina's dad Tommy Thomas, her sister Alanda, and best friend Amanda Phillips left their hotel there for court this morning they were grim-faced, suspecting that the prosecutor and Gabe had cut a deal for a lesser punishment, that they'd never see something they cried out for: a full-blown murder trial with evidence and testimony.

Watson has remarried. His second wife entered the courthouse this morning. In the courtroom 32-year old Gabe Watson, rose for the judge's question:

Watson said not guilty, then entered a plea of guilty to manslaughter. And that was it. The court accepted his plea and he was given four and half years of a suspended sentence. He will actually serve 11-months behind bars in Australia.

Tommy Thomas: It’s total injustice, it’s ludicrous what we have just seen. He was charged with murder, by a senior coroner in the Townseville Supreme Court, that had completed an extensive investigation of the police's investigation. I was just totally destroyed. It’s ludicrous. It’s a slap to the Australian people and the justice system. It’s a slap in the face to the police on both sides, both in us and Australia that spent time investigating this case and the four and the four and a half years here is a joke.

Her family is convinced that Gabe murdered Tina, convinced that he cut a cynical deal with the authorities that let him off with a slap of the wrist.

Alanda: Was in complete shock, complete shock, so complete injustice to Tina, I can't even begin to describe how hard it was to sit there and hear him say that how little my sister life was valued to them. It was very painful.

The Australian investigators who'd labored five and a half years on the case couldn't comment on the manslaughter plea, but Detective Lt. Brad Flynn of Helena, Alabama, was free to tell the cameras and reporters just what he thought.

Detective Flynn: I am, I very shaken . You dedicate yourself, like, five and half years of your life to the case and you want to see resolution, you want to see some closure, you didn't get that today. Not for me but for her family, we didn't get it.

Tina's best friend Amanda:

Amanda: I never thought it would be this minimal. Michael Vick will have spent more time in jail for dogs. Then Gabe will have spent time for Tina. And she was a person.

At the heart of what Gabe Watson pleaded guilty to was this: The certified rescue diver said he didn't murder Tina, but he was guilty of being an irresponsible dive buddy. He was guilty of manslaughter for not helping her with her buoyancy vest, getting her weights dropped, letting her slip away from his grasp.

The diver from the boat who actually recovered Tina from a 100-feet down, Wade Singleton, said he thought today's manslaughter plea allowed Gabe to get off light. He, for one, would like to have seen a murder trial.

Wade: Well, to put it simply, to leave some one down there, invasively signing a death warrant, you are leaving them to die as long as they are underwater and they're not breathing there is no chance of survival so the most important thing is if that person is in trouble they need to be gotten to survive.

Neither Watson's family in the States nor his attorneys would discuss today's plea agreement. The Thomas family, Tina's friend and the detective who pursued the case for years will return to Alabama now with the taste of ashes in their mouth.

Amanda: Whether or not this was a murder or a horrific accident, there are not just five people affected by this. There are dozens upon dozens of people who are so affected by this and that's the real tragedy.

Exactly what happened that morning on the Great Barrier Reef remains a mystery to them all.

Tommy Thomas: This is in no way shape or form even the beginning find get justice for our daughter.

But a ruling that the bridegroom was simply a bad dive-buddy in no way quenches their thirst for justice.

Dateline wires the home of a volunteer, Jenny, from top to bottom with hidden cameras. Then she called repairmen to her house for a simple problem we created as a test with Jenny's pool. NBC's Chris Hansen reports.